1. Field of the Invention
The present invention relates to an absorbent structure suitable for use in absorbent products. More particularly, the present invention relates to an absorbent structure comprising superabsorbent material, wettable staple fiber, and wettable binder fiber.
2. Description of the Related Art
The purpose of disposable absorbent products is typically body waste management. In order to manage liquid body waste, the absorbent structure within an absorbent product must generally be able to first uptake the liquid into the absorbent product, then distribute the liquid within the absorbent product, and then retain the liquid within the absorbent product.
It is generally important that the absorbent structure uptake the liquid at about the rate of delivery of the liquid to the absorbent product or else the liquid may run off the absorbent structure's surface and not be present for the absorbent structure to distribute and retain within the absorbent product. That is, if the liquid uptake rate of the absorbent structure is less than the delivery rate of the liquid to the absorbent product, there exists the possibility of leakage of the liquid from the absorbent product.
In addition, if the distribution of the liquid by the absorbent structure within the absorbent product is not adequate, the efficiency of the absorbent structure's utilization will be low. Typically, commercially available absorbent products are designed with an excess absolute liquid saturated retention capacity. Thus, the absorbent structure in the absorbent product is often not fully utilized. An increase in distribution efficiency of the liquid by the absorbent material would potentially allow either a higher realized liquid saturation level for an absorbent product using the same amount of absorbent structure or the use of less absorbent structure to achieve the same realized liquid saturation level in the absorbent product without any increase in liquid leakage. The use of less absorbent structure to achieve the same realized liquid saturation level in an absorbent product will typically result in less absorbent product being disposed of to the environment.
Absorbent structures suitable for use in absorbent products are generally well known. Originally, it was a general practice to form absorbent structures comprising an absorbent fibrous matrix entirely from wood pulp fluff, such as a batt of comminuted wood pulp fluff. Given the relatively low amount of liquid absorbed by wood pulp fluff on a gram of liquid absorbed per gram of wood pulp fluff basis, it is necessary to employ relatively large quantities of wood pulp fluff, thus, necessitating the use of relatively large, thick absorbent structures.
In order to enhance the absorbent capacity of such absorbent structures, it is common to incorporate into them a superabsorbent material. Such superabsorbent materials are generally capable of absorbing at least about 10 times their weight in water. The introduction of superabsorbent materials into such absorbent structures allows for the use of less wood pulp fluff, since the superabsorbent material generally has a higher liquid absorption capacity on a gram per gram basis than the wood pulp fluff. Moreover, such superabsorbent materials are less pressure sensitive than wood pulp fluff. Thus, the use of the superabsorbent materials generally allows for the production and use of a smaller, thinner absorbent product.
Absorbent structures generally comprise a relatively low amount (less than about 50 weight percent) of the superabsorbent material. There are several reasons for this. For example, superabsorbent materials employed in known absorbent products have generally not had a liquid uptake rate which would allow them to absorb liquid at the rate at which the liquid is applied to the absorbent products during use. Accordingly, the fibrous matrix of the absorbent structure must often serve as a reservoir which will hold the liquid discharged thereon until the liquid is absorbed by the superabsorbent material. Superabsorbent materials with faster liquid uptake rates can absorb liquid faster, but such superabsorbent materials often exhibit gel blocking. Gel blocking refers to the situation wherein the particles of superabsorbent material deform during swelling and block the interstitial spaces between the particles, or between the particles and the fibrous matrix, thus preventing the flow of liquid through the interstitial spaces. At lower levels of addition of the superabsorbent material, the fibrous matrix serves to keep the particles of superabsorbent material separated from one another and provides a capillary structure which allows a liquid to pass through the fibrous matrix to reach the superabsorbent materials located remote from the point at which the liquid is applied to the absorbent product.
Dispersing such superabsorbent materials in a fibrous matrix at relatively low concentrations, in order to avoid gel blocking, results in the need to locate superabsorbent materials in areas relatively remote from the point at which the liquid is applied to the absorbent product. That is, in order to introduce useful amounts of superabsorbent material into an absorbent structure, and yet disperse such superabsorbent materials sufficiently to prevent gel blocking, it is necessary for the absorbent structures to have relatively large surface areas and to be relatively thick. For the above reasons, it is still typically necessary to use relatively low concentrations of superabsorbent material and enough fibrous matrix to permit the superabsorbent materials to function in the desired manner.